1. Field of the Invention
The present invention relates to a method and a device for picking up a seedling from a seedling tray, and more particularly, for picking up a seedling from a plurality of seedling storage cells formed in a seedling tray.
2. Description of the Related Art
An example of a conventional seedling picking up device for a seedling tray, is disclosed in Japanese Unexamined Patent Publication No. Heisei 7 (1995)-184421.
As shown in FIG. 21, the conventional seedling tray transporting apparatus is constructed with a seedling tray 113, in which a plurality of seedling storage cells 112 are embossed in a sheet form tray body 111, and a transporting member 115 transversely extending between a pair of transporting strips 114, 114 (only one is shown), is inserted between adjacent seedling storage cells 112, 112. The pair of transporting strips 114, 114 are intermittently driven at a predetermined pitch for driving the seedling storage cells 112 by the transporting member 115 to stop each of the seedling storage cells at a predetermined seedling picking up position, at which a seedling picking up claw 116 is disposed.
However, the conventional device encounters the following problems.
(1) With respect to the seedling tray, in addition to a sheet type, in which a plurality of seedling storage cells 112 are embossed, as set forth above, there is a board type, in which a plurality of seedling storage cells recessed in a board form a tray body.
In the conventional transporting device, in which the seedling storage cells 112 are pushed by the transporting member 115 inserted between adjacent seedling storage cells 112, it is not possible to transport the board type cell having a flat bottom surface.
(2) When another sheet type seedling tray which differentiates in the arrangement pitch and the size of the seedling storage cells, is used, it is not possible to register the seedling storage cell to the predetermined seedling picking up position unless the traveling pitch of the transporting strips 114, 114 is significantly altered. Therefore, a complicated exchanging operation becomes necessary when using different types of seedling trays, resulting in a lowering work efficiency.
It is desirable to enable picking-up of the seedling by stopping the seedling storage cell at a predetermined seedling pick-up position even when the arrangement pitches of the seedling storage cells and the sizes are different in the seedling storage cells or the types of the seedling trays are different, such as between the sheet type, board type and so forth. This can be achieved by an apparatus which detects the front end face of the seedling tray in the transporting direction by a tray detecting sensor to stop the first row of the seedling storage cells in the seedling tray at the seedling pick-up position, subsequently calculating a transporting distance of the seedling tray from the detected position of the front end face of the seedling tray in the transporting direction by the tray detection sensor, making judgment whether the calculated transporting distance matches with the arrangement pitch so that the seedling tray is stopped every time when a matching of the transporting distance and the predetermined arrangement pitch of the seedling storage cells is reached and whereby each row of the seedling storage cells are stopped at the seedling pick-up position.
However, in the foregoing transporting device of the seedling tray, irrespective of the actual transporting distance of the seedling tray, the seedling tray is stopped when the arithmetically calculated transporting distance matches with the predetermined pitch. Therefore, it is possible that the actual transporting distance and the calculated transporting distance become inconsistent due to accumulated error of a measured value which is used as a reference in calculation of the transporting distance or a play in the transporting mechanism portion of the seedling tray.
In such a case, the position of the seedling pushing rod and the rod insertion hole in the bottom portion of the seedling storage cells of the seedling tray cause an offset of insertion of the seedling pushing rod into the seedling storage cells and thus make it impossible to pick-up the seedling from the seedling tray.
In addition, in the transporting path of the seedling tray, it is typical to arrange a guide rail or the like so that the seedling tray may travel in straight. However, in a certain setting of the gap between the guide rail and the seedling tray, the seedling tray may be transported in a tilted manner. In such a case, the seedling pushing rod and the rod insertion hole in the bottom portion of the seedling storage cells of the seedling tray become offset to each other to make it impossible to pick-up the seedling from the seedling tray. Also, transportation of the seedling tray in the tilted manner can be caused when the tray is worn or deformed.